code: def test_empty_9137() -> None:
      out = (
          pl.DataFrame(
              {"id": [], "value": []},
              schema={"id": pl.Float32, "value": pl.Float32},
          )
          .group_by("id")
          .agg(pl.col("value").pow(2).mean())
      )
      assert out.shape == (0, 2)
      assert out.dtypes == [pl.Float32, pl.Float32]
  
file_path: polars/py-polars/tests/unit/test_empty.py
imports: import pytest
  import polars
  from polars.testing import assert_frame_equal, assert_series_equal
label_desc: Use image node_id 8 for calling a global function with example usage: test_empty_9137() without return types